This invention relates to an acid based antifreeze coolant formulation for heavy duty applications such as for diesel engines which may be used for inhibition and prevention erosion and corrosion of aluminum and the corrosion of other metals exposed to an aqueous liquid in automotive coolant systems. The formulation further inhibits mineral scale. It may be packaged as an ethylene glycol based additive or in a concentrated corrosion inhibition package for use in new engines or as an additive as for reinhibition of used coolant.
Automotive engine cooling systems consist of many metals including aluminum, steel, cast iron, brass, copper and solder. Engine coolants must not only provide freeze protection but corrosion inhibition as well. Often the components are thin walled for improved heat transfer making them more vulnerable to corrosive attack and subsequent failure. Corrosion products and deposits can interfere with heat transfer. Ultimately overheating and engine failure from thermal related stresses are possible.
Antifreeze/coolant technology traditionally uses silicate as a corrosion inhibitor. Silicates are particularly useful in protecting aluminum automotive cooling system components.
Traditionally antifreeze/coolant is sold at nearly one-hundred percent glycol content. This concentrated packaging allows for flexibility so that the user can dilute the antifreeze/coolant, as needed, with available water to obtain the required freeze/boil protection. However, corrosion protection is needed over the entire dilution range. Moreover, the present invention may be formulated as an additive concentrate package for direct application to existing used diluted antifreeze/coolant mixtures in engines to stabilize and replace components of the coolant.
In modern automotive engineering, many engine components are fabricated from aluminum. Engine coolants, primarily ethylene glycol or propylene glycol based solutions, must transfer heat from operating aluminum engines while inhibiting corrosion. Older automotive engines did not have aluminum components and thus, the traditional antifreeze/coolant compositions may produce corrosion in heat rejecting aluminum or aluminum alloy components. The cavitation erosion-corrosion of aluminum water pumps upon exposure to aqueous systems such as water-cooled internal combustion engine coolants is a relatively new development.
U.S. Pat. No. 4,717,495 by Hercamp et al., hereby incorporated by reference, teaches a sodium-free buffer solution. U.S. Pat. No. 4,548,787 discloses the use of a combination water soluble phosphate with tungstate, selenate and molybdate for protection against cavitation erosion-corrosion on aluminum. U.S. Pat. No. 4,404,113 discloses the use of polyhydric alcohols as corrosion inhibiting and cavitation reducing additives for coolants.
U.S. Pat. No. 4,440,721, discloses the combination of a water-soluble phosphate with a water soluble molybdate, tungstate, or selenate for providing a protective effect against the cavitation corrosion of aluminum in aqueous liquids.
Engine coolants based on inorganic components like silicates, phosphates, nitrates, borates and nitrites have problems due to inhibitor depletion. The depletion to these components, particularly the silicates have lead to concerns about lifetime. More over, high solids loading from inorganic salts presents potential deposit issues. The precipitating solids may scale and plug passages within the engine coolant system.
Recently the automotive industry has developed engine coolants based primarily on carboxylic acid technology. Many U.S. and foreign patent references disclose the use of various monobasic or dibasic acids or salts as corrosion inhibitors. For example, in U.S. Pat. No. 4,647,392, Darden teaches a synergistic combination of 0.1 to 15 weight percent of C5 to C6 aliphatic monobasic acid with the same amount of C5 to C6 dicarboxylic acid and 0.1 to 0.5 weight percent of a hydro carbonyl triazole. The triazole is typically tolytriazole or benzotriazole. The acids are present as salts in an alkaline solution. In U.S. Pat. No. 4,946,616, Falla teaches a mixture of two aliphatic dicarboxylic acids with a hydrocarbyl triazole. In U.S. Pat. No. 4,587,028, Darden discloses two to five weight percent of an aromatic monocarboxylic acid, benzoic acid, with 0.5 to 1.5 weight percent of a C8 to C12 aliphatic carboxylic acid and an alkali metal nitrate. British military specification TS 10177 (Al39), March of 1978, call for 4 to 4.5 weight percent of sebacic acid(aliphatic dicarboxylate) and 0.25 to 0.30 weight percent of benzoytriazole. In U.S. Pat. No. 4,382,008, Boreland has combined an aromatic monocarboxylic acid with C7 to C13 dibasic organic acids and conventional inhibitors such as borate and silicate to prepare formulations. However, the use of these additives increase the overall cost of the formulation.
U.S. Pat. No. 5,366,651 by Maes et al. emphasizes that imidazole serves as a buffer to assist in pH control and serve as the buffer in carboxylic acid based antifreeze formulations. Imidazole is an unsubstituted triazole containing two nitrogen molecules providing a very active triazole molecule to combine with hydrogen providing a neutralizing or buffering capability.
In summary, a wide number of organic acids have been successfully used in various combinations among themselves and with more common components. Typically acids are used at the several percent level if common inhibitors are not present. The presence of hydrocarbyl triazoles indicates that yellow metals such as copper and brass, and solder must be protected separately. The carboxylates are primarily inhibiting ferrous metals and aluminum in these formulations. Despite the successful lab data reported, questions remain about the ability of full acid technologies like Darden and Falla to protect solder and prevent cavitation erosion-corrosion on aluminum in engine applications. Further, the addition of large quantities of inorganic salts to correct these deficiencies negates the low solids benefit.
None of the above references provide a means for obtaining a long life silicate acid-based antifreeze composition as does Applicant""s present invention. Alkali metal molybdates and the soluble salts of tungstic and selenic acids have been used in antifreeze compositions to prevent the corrosion of metals, particularly cast iron, and soluble salts of molybdic, tungstic and selenic acids act to retard the corrosion of aluminum, particularly the cavitation erosion-corrosion of aluminum water pumps. The instant invention combines selected organic acids, azoles, nitrate and/or nitrite salts, molybdates, stabilized silicates and transition metal compounds provide a synergistic protective effect against the cavitation corrosion of aluminum in aqueous liquids reducing the corrosion rate and is effective at relatively low concentrations and varying pH ranges. The addition of selected organic acids not only significantly reduces glycol based coolant cavitation erosion-corrosion, heat rejecting aluminum corrosion, and hard water precipitates and scale, it has been discovered that utilization of selected organic acids in combination with certain additives enhance secondary silicate stabilization leading to improvement in aluminum corrosion protection and coolant life.
Moreover, the organic acids conventionally used with antifreeze coolants are based on dicarboxylic acids or combinations thereof. The present invention provides a means to utilize the less expensive monocarboxylic acids to obtain superior corrosion protection to the dicarboxylic acids either alone or in combination with other organic acid additives.
The present invention has met the above-described need by providing an antifreeze/coolant composition using selected additives which reduce corrosion over the entire dilution range without creating precipitates. This composition is soluble in water, alcohol, and alcohol/water mixtures, is compatible with other commonly used antifreeze/coolant components, does not corrode or damage automotive cooling systems and is effective at relatively low concentrations. In addition, the present corrosion inhibition formulations are effective in reducing corrosion in the entire range of cooling system metals, including heat rejecting aluminum, aluminum alloys, copper, steel, cast iron, brass, solder and the like.
The novel antifreeze formulation of the instant invention comprises a mixture of ethylene or propylene glycol, an organic acid, preferably a monobasic aliphatic organic acid, azoles, low levels of molybdates, nitrite and/or nitrate salts, polyvinylpyrrolidone, a hydroxide salt, silicates and/or siloxane stabilized silicates with transition metal compounds which provide a synergistic protective effect against the cavitation corrosion of aluminum in aqueous liquids reducing the corrosion rate and is effective at relatively low concentrations and varying pH ranges. The addition of selected organic acids not only significantly reduces glycol based coolant cavitation erosion-corrosion, heat rejecting aluminum corrosion, and hard water precipitates and scale, it has been discovered that the aliphatic monobasic organic acid in combination with siloxane stabilized silicates enhance secondary silicate stabilization leading to improvement in aluminum corrosion protection and coolant life when utilized with selected amounts of the above-identified additives. The formulations are particularly suitable for diesel engine applications.
More particularly, the present heavy duty formula for diesel engines has met the above-described need by providing supplemental additives such as nitrate and nitrite salts, silicates and/or siloxane stabilized silicates, and a polyvinylpyrrolidone at 15%, to a light duty formula for automotive use utilizing an ethylene based glycol antifreeze/coolant composition using a combination of a selected monocarboxylic acid, preferably an aliphatic carboxylic acid such as 2-ethylhexanoic acid, a hydroxide such as potassium hydroxide at 45%, a hydrocarbyl tolytriazole such as sodium tolytriazole at 50%, low levels of molybdate additives such as a sodium molybdate dihydrate, and optionally defoamers which reduce corrosion over the entire dilution range without creating precipitates.
The instant antifreeze formulation having a mixture of ethylene or propylene glycol, monobasic organic acid, azoles, and low levels of molybdates may also provide a synergistic protective effect against the cavitation corrosion of aluminum in aqueous liquids reducing the corrosion rate which is effective at relatively low concentrations and varying pH ranges. The combination of monobasic organic acid, hydrocarbyl tolytriazole, and low levels of molybdates not only significantly reduces glycol based coolant cavitation erosion-corrosion, heat rejecting aluminum corrosion, and hard water precipitates and scale, it has been discovered that the combination leads to improvement in aluminum corrosion protection and coolant life when utilized with selected amounts of the above-identified additives. Thus, the formulation is particularly suitable for automotive gasoline and diesel engine coolant applications.
A preferred embodiment of the present invention provides for an antifreeze/coolant solution for inhibiting the corrosion of metals and inhibiting mineral scale based on 100 parts by weight of said glycol-based solution comprising an effective amount which is usually from about 0.1 to about 10.0 weight percent of a monobasic carboxylic acid compound; an effective amount of a salt which is at least one selected from the group comprising sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, lithium nitrate and combinations thereof in an amount up to about 10.0 percent by weight and more particularly from about 0.01 to 10.0 percent by weight; and/or an effective amount of a salt which is at least one selected from the group comprising sodium nitrite, potassium nitrite, magnesium nitrite, calcium nitrite, lithium nitrite and combinations thereof in an amount of up to about 10.0 percent by weight, and preferably from about 0.01 to 10.0 percent by weight; an effective amount which is usually from about 0.01 to about 5.0 weight percent of an azole compound selected from the group comprising a sodium mercaptobenzothiazole, sodium tolytriazole, water-soluble triazoles, benzotriazole, tolyltriazole, or an effective amount of an azole compound having at least three nitrogen molecules which is usually an amount of from about 0.01 to about 10.0 percent by weight; an effective amount of a silicone, silicate, and/or silicone-silicate siloxane copolymer which is usually an amount of about 0.01 to about 10.0 percent by weight; an effective amount which is usually from about 0.001 to about 5.0 percent by weight of a polyvinylpyrrolidone; an effective amount which is usually from about 0.001 to about 10.0 weight percent of a transition metal compound selected from the group comprising disodium salt dihydrate of molybdic acid, molybdenum trioxide, silicoheteropolymolybdates and/or phosphorohetero-polymolybdates, sodium molybdate, potassium molybdate, lithium molybdate, ammonium molybdate, ammonium dimolybdate, and ammonium heptamolybdate; and an effective amount of a glycol compound selected from the group comprising ethylene glycol, diethylene glycol, propylene glycol, methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol and combinations thereof making up the balance of the solution.
It is an object of the present invention to provide corrosion inhibition formulations for antifreeze/coolant compositions with selected monobasic carboxylic acid additives for reducing glycol based coolant cavitation erosion-corrosion.
It is another object of the present invention to provide corrosion inhibition formulations for antifreeze/coolant compositions with selected monobasic carboxylic acid additives for enhancing silicate stability providing an improvement in coolant life.
It is another object of the present invention to provide corrosion inhibition formulations which reduce corrosion over the entire dilution range of antifreeze/coolant compositions without creating precipitates.
It is an additional object of the present invention to provide corrosion inhibition formulations which are effective in reducing corrosion in the entire range of cooling system metals.
It is an additional object of the present invention to provide corrosion inhibition formulations which are effective in reducing heat rejecting aluminum corrosion.
It is an additional object of the present invention to provide corrosion inhibition formulations which are effective in reducing hard water precipitates and scale.
It is a further object of the present invention to provide corrosion inhibition formulations which are soluble in alcohol, alcohol/water mixtures and water alone.
It is an object of the present invention to provide corrosion inhibition formulations which are compatible with commonly used antifreeze/coolant components.
It is another object of the present invention to provide corrosion inhibition formulations which are effective at relatively low concentrations.
It is an additional object of the present invention to use organic acids in the corrosion inhibition formulations to reduce the corrosion.
It is a further object of the present invention to utilize at least one nitrite, at least one nitrate, or a combination of nitrites and nitrates to maximize the protection of ferrous metals and minimize pitting thereof.
It is a further object of the present invention to utilize molybdate to protect against erosion and cavitation of aluminum.
It is a further object of the present invention to provide corrosion inhibition formulations for antifreeze/coolant compositions utilizing an acid based formula in combination with a stabilized silicate for enhancing coolant stability providing an improvement in coolant life for heavy duty coolant applications in diesel engines.
It is an additional object of the present invention to utilize a monobasic carboxylic acid and a hydrocarbyl triazole to allow a low level of molybdate to be utilized in the corrosion inhibition formulations to reduce the corrosion.
These and other objects of the present invention will be more fully understood from the following description of the invention.